This invention relates to catheters and in particular to guidewire-directed dilation balloon catheters, for use in the performance of percutaneous transluminal peripheral and coronary angioplasty.
In 1977 Dr. Andreas Gruentzig first used a balloon-tipped flexible catheter to percutaneously dilate a region of stenosis within the coronary artery of a patient with atherosclerotic heart disease. Since that time, the incidence of percutaneous transluminal coronary angioplasty has increased exponentially. Over the course of the past eight to ten years, the performance of this procedure has become routine within many major medical centers throughout the world. With the advent of improved technology and operator skill, the indications for this procedure have increased substantially.
U.S. Pat. No. 4,195,637 describes the original catheter conceived by Dr. Gruentzig. By current standards, the design of this device affords limited directional control. Use of this device was largely abandoned in the early 1980's following the introduction of "over-the-wire" catheters. U.S. Pat. No. 4,299,226, describes an over-the-wire catheter. Over-the-wire catheters have remained the most popular angioplasty catheters to date, despite the advent of a variety of more recently developed "non-over-the-wire" catheter systems. The popularity of over-the-wire catheters stems largely from the fact that these catheters remain the safest and, with minor exception, the most steerable catheters among the prior art.
The primary limitation of the various over-the-wire catheters of the prior art concerns their respective crossing profiles. For the purposes of this discussion, the crossing profile of a balloon catheter system is defined as the maximal profile of the deflated balloon component of the system. Relative to the more recently developed non-over-the-wire devices, over-the-wire devices have substantially larger crossing profiles. Hence, these catheters create more resistance during manipulation within the confines of critical stenoses, require more force to install across lesions and cause more intravascular trauma during this process compared to the more recently developed, lower profile non-over-the-wire devices.
Considerable effort has been directed toward the development of over-the-wire systems with progressively lower crossing profiles. Virtually all of the progress to date, however, has resulted from progressive miniaturization of the components contained within these devices. The use of state-of-the-art plastics has permitted the manufacture of these devices with progressively thinner walls, and the development of new technologies has permitted the construction of these devices with progressively smaller caliber lumens. Relatively little benefit has resulted from efforts to modify the fundamental design of over-the-wire devices which has remained essentially unchanged to date.
The factors that influence the magnitude of the crossing profile of an over-the-wire device of the prior art include: (1) the inflated profile of the balloon component, (2) the thickness of the walls of the balloon component and (3) the profile of the inner member that extends through the confines of the balloon component.
The first factor, the inflated profile of the balloon, impacts the crossing profile of over-the-wire angioplasty dilatation balloon catheters because the materials most suitable for use in the construction of the balloon components of angioplasty catheters are relatively noncompliant. Further progress in reducing the crossing profile of an over-the-wire system of the prior art is constrained by the need to maintain the inflated balloon profile of the device within the therapeutic range (i.e., 1.5-4.0 mm for coronary catheters and 4-10 mm for peripheral vascular catheters).
The second factor, the thickness of the walls of the balloon component, also impacts the crossing profile of over-the-wire devices of the prior art. The crossing profile of over-the-wire catheters has been reduced by decreasing the thickness of the walls of the balloon component. However, the wall thickness of the balloon component must remain within a range that confers satisfactory pressure tolerance and balloon durability.
The third factor influencing the crossing profile is the profile of the inner member of the balloon. The luminal profile of the inner member of the balloon component of prior art over-the-wire systems must exceed the maximal profile of the guidewire mandrel contained within the system to enable bidirectional separation of the catheter component from the guidewire component of these systems. Separability of the guidewire component form the catheter component constitutes one of the fundamental functional advantages of this class of catheters. This feature affords the opportunity to accomplish a catheter exchange without the need to sacrifice intraluminal access during this process. The factors that influence the profile of the balloon component inner member of prior art devices include: (a) the maximal profile of the guidewire mandrel contained within the device; (b) the magnitude of the catheter-guidewire clearance within the vicinity of the balloon component of the catheter; and (c) the thickness of the walls of the balloon component inner member. In some prior art catheters the maximal (i.e. proximal) profile of the guidewire mandrels contained within these devices has been reduced with the aim to reduce the crossing profile of the composite device. Unfortunately, this approach reduces both the "trackability" and the directional control or "steerability" of these systems. The trackability of a catheter is the facility with which a catheter can be advanced over a guidewire. It varies as a function of the rigidity of the guidewire contained within the system, which for prior art devices varies as a function of the profile of the guidewire mandrel. Reducing the profile of the guidewire mandrel compromises the rigidity of the guidewire and adversely affects the trackability of the composite system.
Reducing the proximal profile of the guidewire mandrel invariably compromises the directional control of the composite system because the steerability of a prior art over-the-wire system varies as a function of the profile of the proximal aspect of the guidewire mandrel contained within the system. Hence, further progress in reducing the profile of the balloon component inner member and ultimately the crossing profile of an over-the-wire dilatation balloon delivery system is constrained by the need to: maintain the proximal profile of the guidewire mandrel within a range that confers satisfactory trackability to the system, maintain the proximal profile of the guidewire mandrel within a range that confers satisfactory directional control to the system, and maintain the profile of the guidewire channel within the balloon component inner member sufficiently large to accommodate the proximal profile of said guidewire mandrel.
The magnitude of the catheter-guidewire clearance within the vicinity of the balloon also impacts the profile of the balloon component inner member and hence the crossing profile of the composite device. Reducing the magnitude of the catheter-guidewire clearance reduces the directional control of the device. The directional control of an over-the-wire system of the prior art varies directly as a function of the magnitude of rotational torque that can be delivered to the distal aspect of the guidewire. The efficiency with which this rotational torque can be transmitted within the confines of an over-the-wire system of the prior art varies, in part, with the magnitude of the catheter/guidewire clearance. Further progress in reducing the crossing profile of an over-the-wire device of the prior art is constrained by the need to maintain the magnitude of the catheter-guidewire clearance within a range that permits satisfactory guidewire-mediated torque delivery and hence satisfactory directional control.
The thickness of the walls of the balloon component inner member also impacts the profile of the inner member and hence the crossing profile of the composite device. The inner member confers column strength (i.e., resistance to coaxial compression) to the catheter. The magnitude of column strength conferred by the inner member varies directly with the thickness of the walls of the inner member (provided that comparable materials are used in the construction of the respective inner members). The column strength of a particular device profoundly influences the feasibility with which the device can be negotiated within the confines of critically stenotic lesions. Prior art catheters with thinner balloon component inner member walls, the catheters generally suffer from reduced pushability or column strength. Any further reduction in the crossing profile of conventional over-the-wire devices is constrained by the need to maintain the thickness of the walls of the inner member within a range that confers satisfactory column strength to the composite system.
In short, using prior art techniques there is a lower limit to the crossing profile that can be achieved in the construction of functionally suitable over-the-wire catheters, given the constraints inherent to the design of these systems and the limitations of current technology. This circumstance largely accounts for the fact that the majority of current generation over-the-wire catheters are similar in crossing profile.
Given the aforementioned limitations, a variety of more recent catheter configurations have been developed that enable the construction of guidewire-directed balloon delivery systems with lower crossing profiles. These more recently developed systems include: (1) "semi-movable" catheter systems, (2) "fixed-wire" catheter systems and (3) "balloon-on-a-wire" catheter systems. These devices are distinguished by virtue of the relative mobility of the guidewire components contained within these systems. "Semi-movable" catheters permit full rotational and limited coaxial mobility of the guidewire components relative to the catheter components of these systems. U.S. Pat. No. 4,616,653 describes a semi-movable system. "Fixed-wire" catheter systems permit variable rotational mobility of the guidewire components relative to the catheter components of these systems and yet they afford no coaxial catheter-guidewire mobility. U.S. Pat. No. 4,582,181 describes a fixed-wire system. "Balloon-on-a-wire" devices do not provide any mobility of the guidewire components relative to the balloon components of these systems. Directional control of these devices is accomplished by rotating the entire device. International Patent Application No. PCT/US86/00983 describes a balloon-on-a-wire device.
Each of these systems are easier to prepare, and more convenient to use relative to over-the-wire systems because they contain pre-installed guidewires. Each of these devices can be advanced within the confines of critical lesions with greater facility relative to over-the-wire devices of the prior art because they have lower crossing profiles.
The structural advantages of non-over-the-wire devices largely have been achieved at the expense of functional trade-offs. None of these systems permit separation of the guidewire components from the respective catheter components. Hence, their use obligates sacrificing intravascular access in the event that a catheter exchange is required. This circumstance, in turn, mandates the renegotiation of a lesion with a second guidewire during the course of a catheter exchange, a process that contributes to the duration, complexity and morbidity of the procedure.
Selected fixed-wire and all balloon-on-a-wire systems of the prior art also afford compromised guidewire mobility and hence, directional control and reach and ccross potential relative to over-the-wire and semi-movable systems. This disadvantage arises because the majority of these devices contain bonds between the balloon and guidewire components of these systems. U.S. Pat. No. 4,582,181 describes a fixed-wire device that contains a bond between the balloon and guidewire components of the device. International Patent Application No. PCT/US86/00983 describes a balloon-on-a-wire device that similarly contains a bond between the balloon component and guidewire component of the system.
The inability to advance and withdraw the guidewire component independently of the balloon component of these systems further complicates the process of performing intraoperative angiography. Typically, the balloon component of a catheter/guidewire system must be withdrawn completely from the vasculature to enable the performance of intraoperative angiography with satisfactory resolution. Intraoperative angiography is commonly performed following balloon dilatation, during the course of an angioplasty procedure, to assess the impact of the procedure on the configuration of the lesion requiring dilatation.
Semi-movable and over-the-wire devices readily permit intraoperative angiography. The catheter components of these systems can be withdrawn over the respective guidewire components, to enable the performance of intraoperative angiography, without sacrificing intraluminal guidewire access during this process. In the event that additional dilatation is required following angiography, the balloon components of these systems can be readvanced over the respective guidewire components across the confines of the respective stenoses and re-inflated. Because fixed-wire and balloon-on-a-wire systems of the prior art do not afford coaxial guidewire mobility, the use of these devices obligates sacrificing intraluminal access during the performance of intraoperative angiography. Hence, their use exposes the patient to the added risk associated with renegotiation of the lesion, when subsequent dilatation is required.
In summary, there currently exist a variety of functional and structural trade-offs intrinsic to the designs of prior art dilatation balloon catheter systems. Over-the-wire systems afford safety and directional control at the expense of crossing profile. Semi-movable systems of the prior art afford directional control and modest advantages in terms of crossing profile at the expense of procedural safety. Selected fixed-wire and balloon-on-a-wire systems afford significant advantages in terms of crossing profile at the expense of procedural safety and directional control. Clearly, there exists a need for a catheter configuration that enables the construction of a guidewire-directed dilatation balloon delivery system that offers: (1) the crossing profile of a balloon-on-a-wire or fixed-wire device, (2) the coaxial/rotational guidewire mobility (i.e. steerability), and convenience of a semi-movable device, and (3) the procedural safety of an over-the-wire device.